INSTRUCTION MANUAL
CAUTION: Read All Instructions Before Operating Equipment
MFJ ENTERPRISES, INC.
300 Industrial Park Road
Starkville, MS 39759 USA
Tel: 662-323-5869 Fax: 662-323-6551
COPYRIGHT 2005 MFJ ENTERPRISES, INC.
C
Model MFJ-652
VERSION 1A
DISCLAIMER
Information in this manual is designed for user purposes only and is not
intended to supersede information contained in customer regulations, technical
manuals/documents, positional handbooks, or other official publications. The
copy of this manual provided to the customer will not be updated to reflect
current data.
Customers using this manual should report errors or omissions,
recommendations for improvements, or other comments to MFJ Enterprises, 300
Industrial Park Road, Starkville, MS 39759. Phone: (662) 323-5869; FAX: (662)
323-6551. Business hours: M-F 8-4:30 CST.
MFJ-652 hamProAudio
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TABLE OF CONTENTS
TOPIC PAGE
1. TABLE OF CONTENTS 2
2. LIST OF FIGURES 2
3. INTRODUCTION AND FEATURES 3
4. TYPICAL SPECIFICATIONS 4
5. SYSTEM CONTROLS 5
a. FRONT PANEL JACKS AND CONTROLS 5
b. REAR PANEL JACKS AND CONTROLS 6
6. SYSTEM SETUP 7
a. INTERNAL HEADERS 7
b. INTERNAL JUMPER BLOCK 8
c. CABLES 10
d. POWER 10
e. HEADPHONES 10
f. RADIO AUDIO 10
7. THEORY OF OPERATION 11
8. MFJ-652 EASY-START INSTRUCTIONS 12
9. IN CASE OF DIFFICULTY 15
10.TECHNICAL ASSISTANCE 15
LIST OF FIGURES
Figure 1 Front Panel Jacks and Controls 5
Figure 2 Rear Panel Jacks and Controls 6
Figure 3 Internal Headers 7
Figure 4-10 Internal Jumper Blocks 8-12
Figure 11 Functional Diagram 15
Figure 12 Schematic 20
LIST OF TABLES
Table 1 Microphone Pinout 13
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INTRODUCTION & FEATURES
INTRODUCTION
The MFJ-652 hamProAudio Transmit Audio Equalizer is a quality microphone
audio equalizer. With 4 adjustable center frequencies you can adjust your
microphone audio for rich full audio for rag chewing. For serious DXing you can
increase the high and decrease the lows for a signal that really punches through
the pile-ups.
hamProAudio Quality: Designed with the serious ham in mind. Not just a
typical audio equalizer being used with an amateur station. Choice of
components and extensive RF filtering and bypassing allows for a unit that is
designed to be used in a RF environment.
Fully adjustable Gain Amplifiers: You have full control of the input level from
your microphone and output level to your radio. With MFJ’s LED monitoring you
set the output level once and then feel confident that you are driving your radio
with the perfect level no matter how much you increase or decrease the gain of
each section of the equalizer.
Audio Pass Through from your Radio: No need to switch the headphones
from the MFJ-652 to the radio. At the push of a button you can instantly switch
from normal operation to a test mode. This allows you to adjust the settings
without going on the air with the built in monitor amplifier.
By-pass Function: Switch the MFJ-652 in or out and you still have the received
audio in the headphones.
Multiple Outputs: The MFJ-652 has multiple audio outputs. Microphone audio
is fed out through the RJ-45 connector or through the 3.5 -mm Auxiliary Output
Jack.
Rugged Construction: Attractive all-metal cabinet, conservative component
selection, space age SMD Circuitry and extensive RF filtering ensure solid
performance for years to come. Fully covered by MFJ’s “No Matter What” one
year limited warranty.
Before attempting to operate your MFJ-652, please read the manual thoroughly.
It contains important details about setting up your unit to obtain the best
performance.
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INTRODUCTION & FEATURES
TYPICAL SPECIFICATIONS
Input source……………………Dynamic or Electret mic low or high Z
Stereo or Monaural radio audio.
Sound card or Modem
Output ………………………….Adjustable signal level. RJ-45 or 3.5 –mm
Frequency Range……………..300, 600, 1200, 2400 Hz center
Overall Response……………..100-5000 Hz
Total harmonic distortion …….1% maximum, <0.2% typical
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SYSTEM CONTROLS
MFJ-652 JACKS AND CONTROLS
2400 Hz1200 Hz600 Hz300 Hz
MFJ Voice Band Microphone EqualizerhamProAudio™
MFJ-652
+
-
MIC IN
ON
OFF/
BYPASS
MONITOR
OUTPUT
+
-
+
-
Max Min Max Min
INPUT LEVEL POWER OUTPUT LEVEL
+
-
EQUALIZER
0 0 0 0
Figure 1: MFJ-652 Front Panel Jacks and Controls
1. RJ-45 Microphone Input Jack: Accepts input from a Standard RJ-45
microphone.
8-Pin Microphone Input Jack: Accepts input from a standard 8 pin
microphone.
2. 300 Hz: Cuts or emphasizes lowest speech frequencies.
3. 600 Hz: Cuts or emphasizes mid-range speech frequencies.
4. 1200 Hz: Cuts or emphasizes upper-range speech frequencies.
5. 2400 Hz: Cuts or emphasizes syllabant sounds and adjacent channel
“chatter”.
6. Input Level LED: Allows for easy setting of the input level to the
equalizer. Never worry about overdriving the equalizer.
7. Monitor Output Level: Easily set the output monitor to a comfortable
level in the headphones.
8. Output Level LED: Set the output level trimpot one time and you will
have easy control of the signal sent to your radio.
9. Output Level Control: Adjusts the level sent to you radio.
10. Power LED: Visual indication whether the unit is in line or not.
11. On & Off/Bypass Switch: Allows you to use either your microphone
direct or through the MFJ-652.
1 2 3 4 5 6 7
9
8 10 11
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SYSTEM CONTROLS
POWER
12VDC
OUTPUT
LED
LEVEL
EXTERNAL
PTT
SWITCH
AUX.
AUDIO
OUTPUT
AUX.
AUDIO
INPUT
INPUT
LED
LEVEL
MIC
OUT
RECEIVED
AUDIO
INPUT
MFJ ENTERPRISES, INC.
STARKVILLE, MS USA
FROM
MFJ-652
FROM
RADIO
OUT
HEADPHONE
AUDIO
Figure 2: MFJ-652 Rear Panel Jacks and Controls
1. Power: Accepts 2.1 –mm power plug to supply 12-15 volts to the unit.
2. Output LED Level adjust: Sets the level at which the output led
illuminates.
3. From Radio/From MFJ-652: This switch allows the audio to be fed from
the radio to the headphones or in the test mode for the audio from the
microphone to be fed to the headphones for setting the MFJ-652.
Additionally in the test mode the PTT is disabled allowing you to key the
microphone without keying the radio.
4. Headphones Out: Allows you to use a pair of ¼ stereo headphones.
5. External PTT Input: Accepts a ¼ inch plug from a remote hand switch or
foot switch
6. Auxiliary Output: Accept a 3.5 –mm plug for direct audio output. With
internal jumper set allows PTT also.
7. Input LED Level: Allows for adjustment of the input gain depending on
your microphone.
8. Auxiliary Input: This multifunction input allows for just about anything to
be used with the MFJ-652. Use a Heil boom mic, The MFJ-393 Boom Mic
Headset or even a computer microphone by setting the appropriate
internal jumper.
9. RJ-45 Mic Output: This is where the MFJ-5398 or MFJ-5397MX is
attached.
10. Received Audio Input: This jack allows either stereo or mono (if wired
properly) audio from your radio.
1 2 3 4 5 6 7 9 8 10
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SYSTEM SETUP
INTERNAL HEADERS
Figure 3: MFJ-652 Internal Headers
1. Header 1: This sets the input of the unit to your specific microphone.
Default 1-2 is set to 500-1000 ohms, the standard impedance setting for
most stock microphones. If you need low impedance then move the
jumper to positions 3-4. Remove for high impedance microphones.
2. Header 2: This allows the PTT line to be placed on the ring of the 3.5 –
mm auxiliary input jack. Default is off.
3. Header 3: This header allows phantom voltage to be fed to electret
microphones Default is 0 volts pins 1-2 shorted. Move this jumper to pins
3-4 for 1.5 volts, 5-6 for 5 volts or 7-8 for 8 volts.
4. Header 4: This header allows the phantom voltage set by header 4 to be
passed to the ring of the Auxiliary input jack. Default is off. If used with
standard computer microphone/headphones set to 5 volts.
5. Header 5: This header allows the PTT to be placed on the ring of the 3.5
-mm Auxiliary Output Jack.
6. Header 6: This header places phantom voltage on the microphone input
line and must be shorted for use with microphones that require phantom
voltage.
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SYSTEM SETUP
INTERNAL JUMPER BLOCKS
Refer to Table 1 for common microphones. Consult your owners’ manual to
determine your specific microphone pinout.
Figure 4: MFJ-652 Internal Jumper Blocks
1. Jumper 1: Pass/Thru. This allows you to pass any other lines from the
microphone for feature such as up/down/fast. Normally all lines that are
not being used for the Mic Audio, Mic Ground and PTT line will be
jumpered.
2. Jumper 2: PTT to Radio. Place a jumper on the pin corresponding to the
pin that your radio requires for PTT
3. Jumper 3: Microphone Audio Ground to Radio. Place a jumper on the
pin that corresponds to the pin that your radio requires for the shielded
ground.
4. Jumper 4: Microphone Audio to Radio. Place a jumper on the pin that
corresponds to the pin on your radio that feeds microphone audio to the
radio.
5. Jumper 5: PTT from the Microphone. Place a jumper on the pin number
that corresponds to the pin of your microphone that supplies the PTT line
to the radio.
6. Jumper 6: Microphone Audio Ground. Place a jumper on the pin number
that corresponds to the pin that supplies the shielded ground from the
microphone.
7. Jumper 7: Microphone Audio Input. Place a jumper on the pin number
that corresponds to the pin that supplies microphone audio.
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SYSTEM SETUP
INTERNAL JUMPER BLOCKS
The Jumper Installation diagrams within this instruction manual will help you in
setting up your MFJ-652 to match your radio. If your radio is not listed with the
diagram, it means that we have not verified your radio to use that diagram. You
can try to install jumpers as indicated. If that does not work, please refer to the
radio manual to identify the MIC pin assignment for you radio then follow the
instructions given at the end of this section in the MFJ-652 instruction manual to
install the jumpers.
Refer to this figure for the pin numbering 1-8 on the
internal jumper blocks. The RJ-45 connector is
numbered with the clip down. Note the position of the
key for the 8 pin round mic jack this could be rotated in
your particular unit.
ICOM 8-Pin Round Microphone Setup:
IC-255, 288, 28, 290, 38A, 375, 707, 718, 725, 726, 728, 729, 730, 735, 737, 745, 746,
746PRO, 751, IC-756, 756PRO, 756PROII, 775DSP, 761, 78, 781, 910H
This diagram may cover
some other radios in the
ICOM product line with 8-pin
round microphone jack.
If there are any Questions
concerning the information
provided, please refer to
your RADIO INSTRUCTION
MANUAL.
MFJ is neither liable nor
responsible for any mistakes
or errors in the information
provided.
Receive Audio is taken from
the Headphone Audio
Output.
Figure 5: ICOM 8-Pin Round Microphone Setup
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SYSTEM SETUP
ICOM 8-Pin Modular Microphone Setup:
IC-207H, 2720H, 2800H, 703, 706, 706MKII, 706MKIIG, V8000
This diagram may cover
some other radios in the
ICOM product line with 8-pin
modular microphone jack.
If there are any Questions
concerning the information
provided, please refer to your
RADIO INSTRUCTION
MANUAL.
MFJ is neither liable nor
responsible for any mistakes
or errors in the information
provided.
Receive Audio is taken from
the Headphone Audio Output.
Figure 6: ICOM 8-Pin Modular Microphone Setup
Figure 7: YAESU 8-Pin Round Microphone Setup
YAESU 8-Pin Round Microphone Setup:
YAESU FT-650, 707, 712, 726, 736, 756, 767, 77, 790II, 700, 840, 890, 990, 1000D
This diagram may cover some
other radios in the YAESU
product line with 8-pin round
microphone jack.
If there are any Questions
concerning the information
provided, please refer to your
RADIO INSTRUCTION
MANUAL.
MFJ is neither liable nor
responsible for any mistakes
or errors in the information
provided.
Receive Audio is taken from
the Headphone Audio Output.
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SYSTEM SETUP
YAESU 8-Pin Modular Microphone Setup:
YAESU FT-817, 857, 897
This diagram may cover
some other radios in the
YAESU product line with 8-
pin modular microphone jack.
If there are any Questions
concerning the information
provided, please refer to your
RADIO INSTRUCTION
MANUAL.
MFJ is neither liable nor
responsible for any mistakes
or errors in the information
provided.
Receive Audio is taken from
the Headphone Audio Output.
Figure 8: YAESU 8-Pin Modular Microphone Setup
Figure 9: KENWOOD 8-Pin Round Microphone Setup
KENWOOD 8-Pin Round Microphone Setup:
TS-50, 60, 140, 430, 440, 450, 570, 660, 670, 680, 690, 711, 780, 811, 850, 870, 930, 940, 950
TM-201A, 201B, 211, 221, 231, 241, 321, 331, 401A, 401B, 421, 431, 441, 521, 531, 541, 621
TM-631, 701, 721, 731, 2530, 2550, 2570, TR-50, 751, 851, TW-4000, 4100
This diagram may cover some
other radios in the Kenwood
product line with 8-pin round
microphone jack.
If there are any Questions
concerning the information
provided, please refer to your
RADIO INSTRUCTION
MANUAL.
MFJ is neither liable nor
responsible for any mistakes
or errors in the information
provided.
Receive Audio is taken from
the Headphone Audio Output
.
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SYSTEM SETUP
KENWOOD 8-Pin Modular Microphone Setup:
TM-251, 255, 261, 451, 461, 641, 642, 732, 733, 741, 742, 941, 942, G707, V7A
This diagram may cover
some other radios in the
Kenwood product line with 8-
pin modular microphone jack.
If there are any Questions
concerning the information
provided, please refer to your
RADIO INSTRUCTION
MANUAL.
MFJ is neither liable nor
responsible for any mistakes
or errors in the information
provided.
Receive Audio is taken from
the Headphone Audio Output
.
Figure 10: KENWOOD 8-Pin Modular Microphone Setup
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SYSTEM SETUP
Radio Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8
Alinco
MIC
AUDIO
PTT DOWN UP 5
VOLTS
AF
OUT
MIC
GND
GND
Icom
MIC
AUDIO
+8
VOLTS
UP/DOWN SQL PTT PTT
GND
MIC
GND
Kenwood
MIC
AUDIO
PTT DOWN UP 8
VOLTS
NC MIC
GND
PTT
GND
Yaesu FT1000
FT847
UP GND DOWN FAST GND PTT MIC
GND
MIC
AUDIO
Yaesu FT-990
FT-1000MP
UP +5
VOLTS
DOWN FAST GND PTT MIC
GND
MIC
AUDIO
Table 1: Common Microphone Pinouts
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SYSTEM SETUP
CABLES
Simply connect your microphone to the appropriate input and use either a MFJ-
5398 for 8 pin Round or MFJ-5397MX for 8 pin Modular connector to the output
on the rear of the unit and attach to your radio. .
Connect your audio from the headphone jack to the 3.5-mm jack on the MFJ-
652. If your only output is mono then simply wire the tip and the ring of the cable
to provide audio to both sides of the headphones.
Connect a foot Switch or Hand Switch to the PTT jack located on the rear of the
unit.
POWER
The MFJ-652 will operate with any well-filtered 10-14 VDC power supply capable
of at least 150 mA. The required power connector is a 2.1 -mm ID, 5.5 mm OD
coaxial power plug.
As this is a quality audio unit, use of an unregulated wall power supply
transformer is not recommended as the unloaded voltages can easily exceed 15
volts and the lack of filtration and regulation can introduce hum and other
components into your signal.
Wire (+) voltage to center and (-) to common.
HEADPHONES
Use stereo headphones rated at 8-40 Ohms impedance. Jacks for either ¼ inch
or 3.5 –mm headphones are included on the rear of the unit. Use of quality
phones will aid in the reproduction of the audio when setting up the unit.
RADIO AUDIO
If your radio provides left and right output for a main and a sub-receiver then use
a stereo 3.5 –mm to the termination that your radio uses.
If your radio provides mono output then either use a stereo 3.5 –mm cable and
connect the tip and ring and then attach the termination that your radio uses.
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THEORY OF OPERATION
MIC
INPUT
RFI
FILTER
IMPEDANCE
MATCHING
PREAMP
BYPASS
EQ
SECTION
300Hz
600 Hz
1200 Hz
2400 Hz
INPUT
LED
COMPARATOR
INPUT
LED
LEVEL
OUTPUT
LED
COMPARATOR
OUTPUT
LED
LEVEL
MONITOR
AMP
JUMPER
ISOLATION
TRANSFORMER
OUTPUT
Figure 11: Functional Diagram
Figure 5 shows the functional diagram of the MFJ-652. Microphone audio is fed
in through J2, J3 or J4. Header 1 sets the impedance for the specific
microphone in use. From there the microphone audio is routed to U1A where it
is amplified and routed to the equalizer section consisting of U2A-U2D. Active
filters U2A-U2D provide four octaves of adjustable audio conditioning at the input
of summing amplifier U1C. Alternatively microphone audio is routed around the
unit with Bypass switch SW1. The output of U1A also feeds U5B the comparator
for the input LED. The output of U1C feed s U5A the comparator for the output
LED.
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EASY-START INSTRUCTIONS
1. Start with the MFJ-652 Equalizer Switch in the OFF/Bypass position.
Using your microphone set your radio’s microphone gain, alc and any
other features to the proper operating conditions and levels. Set the front
panel controls of the MFJ-652 as follows:
300, 600, 1200 and 2400 Hz : 12 o’clock
Output gain: Fully counterclockwise
Monitor gain: Fully counterclockwise.
2. Connect a dummy load to your radio.
3. Set the From Radio/From 652 switch on the rear of the unit to the From
652 position.
4. Turn on the MFJ-652 and while speaking into the microphone adjust the
monitor gain to a comfortable level.
5. While speaking into the microphone adjust the input level trim pot on the
rear of the unit until the input led just illuminates on voice peaks.
6. Place the From Radio/From 652 switch on the rear of the unit to the From
Radio position.
7. While speaking into the microphone slowly increase the Output Gain
Control until the readings on your radio’s meter are the same with the unit
either on or bypassed.
8. Once this level has been set place the unit in the From 652 position and
while speaking into the microphone adjust the trim pot on the rear of the
MFJ-652 until the Output Gain Level LED on the front panel just
illuminates on voice peaks. This allows you to have a handy reference for
setting the Output Level Control under any condition.
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EASY-START INSTRUCTIONS
Some Results of Research on Speech Intelligibility in hearing English
Words
- The frequencies important for speech intelligibility are the consonant sounds
from 500 to 4000 Hz. They contribute 83 % of word intelligibility.
- Frequencies from 500 to 1000 Hz contribute 35 % of word intelligibility and 35
% of sound energy.
- Frequencies from 1000 to 4000 Hz contribute 48 % of intelligibility but have
only 4 % of sound energy.
- In contrast frequencies from 125 to 500 Hz contribute 55 % of sound energy
but only 4 % of word intelligibility.
- In other words, nearly half the speech intelligibility is contained in the 1000 to
4000 Hz frequency range with only 4 % of the speech sound energy.
- On the other hand, the low frequencies 125 to 500 Hz have most of the
speech energy but contribute very little to intelligibility.
How to adjust your Transmit Audio Equalizer for Maximum Speech
Intelligibility:
This is done best on the air with a friend or someone who will give you an honest
opinion. You can initially use the built in monitor amplifier and listen to your voice
in the headphones or have someone else listen to your voice as you adjust the
knobs. But nothing replaces over-the-air reports.
There are four frequency boost (increase in amplitude) and cut (decrease in
amplitude) knobs spaced an octave apart in frequency. The center frequencies
are approximately 300, 600, 1200, and 2400 Hz. With a knob set at 12 o’clock
there is no boost or cut. Turning the knob clockwise boosts an octave of
frequencies by up to 16 dB while counterclockwise rotation give up to 16 dB of
cut.
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EASY-START INSTRUCTIONS
Adjusting your Transmit Audio Equalizer is based on three principles:
First, reduce your speech energy below 500 Hz. These frequencies contribute
only 4% of intelligibility but has 55% of the speech energy. Do this by turning the
300 and 600 Hz knobs fully counterclockwise. This will drastically reduce your
speech in these two octaves. You may need to increase the amplitude in this
range a little by rotating the 600 Hz knob to 9 to 12 o’clock. Use the bypass
switch to compare. Always adjust the output level to maintain proper output to
your radio.
Second, increase your speech energy above 1000 Hz. These frequencies
contribute 48 % of intelligibility but only has 4 % of speech energy. Do this by
turning the 1200 and 2400 knobs fully clockwise. Always adjust the output level
control so you don’t overdrive your radio. Use the bypass switch to compare.
Third, your voice characteristics are unique. Experiment by boosting and
cutting each frequency range based on the two principles above until your find
the right combination that gives your best speech characteristics
Remember – 12 o’clock is flat (no boost or cut), clockwise is boost and
counterclockwise is cut.
Don’t forget to use the bypass switch often to make comparisons.
Remember to adjust the output gain to maintain the proper output level.
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TECHNICAL ASSISTANCE
IN CASE OF DIFFICULTY
[ ] Won’t Power up: Check the polarity and connection to your power supply.
[ ] No microphone audio: Check the Mic Audio Jumper block and the Mic
Ground Jumper block for proper placement of the jumper on the proper header
position. If using a electret microphone ensure the phantom voltage has been
set to the proper level.
[ ] No receiver audio: Check the cabling from your radio to the MFJ-652.
Ensure the Test/Operate switch on the rear of the unit is in the Operate position.
[ ] Station PTT will not function: Check the PTT jumper block. Ensure that
you have a ground between the radio and the MFJ-652 as the Mic Ground is
isolated from the Chassis Ground.
[ ] Noisy audio, Hum: Magnetically induced hum can be caused to any modern
piece of audio equipment by proximity to unshielded power transformers or
equipment that radiated strong AC fields. Another source of hum can be caused
by a ground loop. This is when equipment is connected together but do not have
their grounds well connected. The use of “Daisy Chain” grounding techniques
can contribute to this problem. The use of a single point ground is always
recommended in Amateur Radio installations. Rf floating in the shack can also
contribute to distortion. To determine if you have this problem simply transmit
into a Dummy Load. If the distortion goes away then you have RF in the shack.
TECHNICAL ASSISTANCE
If you have any problem with this unit first check the appropriate section of this
manual. If the manual does not reference your problem or is your problem is not
solved by reading the manual, you may call MFJ Technical Service at 662-323-
0549 or the MFJ Factory at 662-323-5869. You will be best helped if you have
your unit, manual and all information on your station handy so you can answer
any questions the technician may ask.
You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial Park
Road, Starkville, MS39759; by Facsimile (FAX) to 662-323-6551; or by email to
Send a complete description of your problem, an
explanation of exactly how you are using your unit , and a complete description
of your station.
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